1. Field of Invention
Inventive aspects relate in general to medical devices, and more specifically to cannula seals for minimally invasive surgical systems.
2. Art
In minimally invasive surgery, a body cavity is often insufflated to provide additional work room at the surgical site. In order to prevent insufflation gas from escaping through the cannulas that guide minimally invasive surgical instruments into the body, one or more gas-tight seals are typically coupled to the cannula. These gas-tight seals prevent insufflation gas from escaping through an open cannula when no surgical instrument is inserted through the cannula, and they also prevent gas from escaping through the gap between the cannula and instrument shaft when a surgical instrument is inserted through the cannula.
U.S. Pat. No. 6,123,689 (filed Mar. 28, 1997) discloses a “Reusable Cannula with Disposable Seal,” which is an example of a device that performs the basic functions a minimally invasive surgery cannula seal assembly requires. Two annular flanges provide a gas-tight seal against instrument shafts of various diameters inserted through the seal assembly, and a trap door closes to provide a gas-tight seal when the instrument is removed from the seal assembly. An adapter portion may be coupled over the seal assembly to seal against instrument shafts having a diameter smaller than the shaft diameters sealed by the annular flanges. Instrument shafts include shafts used for endoscopes and other surgical accessories, such as obturators.
Although current cannula seals for minimally invasive surgery are generally effective, improvements are desirable. Such improvements include an increased resistance against punctures and tears that may occur as surgical instruments are inserted through the seal and which reduce or prevent effective sealing (especially for thin-membrane, septum-type wiper seals), an effective accommodation of instrument shafts over a wide range of shaft diameters to minimize the need for two or more seals and consequently reduce operating costs, reduced friction against the instrument shaft as it inserts and withdraws through the seal (thus allowing instruments to be teleoperatively controlled with increased precision, allowing more accurate insertion/withdrawal axis force feedback to a teleoperating surgeon by reducing any other forces along the insertion/withdrawal axis, and reducing a tendency for the seal to invert as the instrument shaft reciprocates), reduced part costs, easy and economical manufacturability, and easy assembly both during manufacturing and in use during surgery.